1. Field
This disclosure relates to an apparatus and method for surface-treating carbon fiber by resistive heating.
2. Description of the Related Art
A carbon fiber can have a carbon content of about 90 percent (“%”), or more. The carbon fiber can be produced from a precursor, such as polyacrylonitrile (“PAN”), rayon, pitch, or the like which is stabilized in an oxygen atmosphere, carbonized, and then graphitized at a high temperature of about 1500° C., or more. Carbon fiber materials are high-function and high-strength materials, and can have excellent specific modulus, specific strength, thermal stability, corrosion resistance, conductivity, vibration attenuation, and wear characteristics. Due to such characteristics, carbon fiber materials can be used in various applications, such as aerospace materials, reinforcing materials for engineering or construction, sports or leisure products, automobile parts or structures, pressure vessels, or external materials for electronic devices. In most applications the carbon fiber is not used alone but in a composite including a matrix. The matrix can include a polymer, a ceramic, a metal, or the like. In the composite, the carbon fiber can function as a reinforcing material. The mechanical characteristics of the composite may depend on characteristics of the matrix, characteristics of the reinforcing material, the content of the reinforcing material, and interfacial characteristics between the matrix and the reinforcing material. It is desirable to improve interfacial adhesion between the matrix and the reinforcing material. Improved interfacial adhesion between a carbon fiber reinforcing material and a matrix can contribute to improved strength and weight in a high-strength lightweight composite.
An interfacial shear strength between a matrix and a reinforcing material can be improved using chemical methods or physical methods. In a chemical method, a chemical bonding force between the matrix and the reinforcing material is increased. In a physical method, an interfacial surface area between the matrix and the reinforcing material is increased, thereby increasing a physical bonding force between the matrix and the reinforcing material. In addition, a physical bonding force between a matrix and a reinforcing material including a carbon fiber can be increased by treating the carbon fiber with microwaves or a plasma to increase a surface roughness of the carbon fiber, or by disposing a secondary phase on a surface of the carbon fiber. However, when the surface roughness of the carbon fiber is increased, using microwaves or a plasma, for example, one or more of the characteristics of the carbon fiber can be degraded, although the interfacial shear strength may be increased. On the contrary, when a whiskerization process is performed on a surface of a carbon fiber to increase a thickness and a surface area of an interface between the carbon fiber and the matrix, the characteristics of the carbon fiber may not be affected and the interfacial shear strength can be increased by between about 200% to about 300%. Accordingly, a method of increasing the thickness and the surface area of the interface by whiskerization can be effective for increasing a mechanical strength of a composite, which can be achieved by improving the interfacial shear strength. Accordingly, it is desirable to have a carbon fiber composite having improved interfacial shear strength, as is an improved method to provide whiskers on a carbon fiber surface.